Electronic control for a hydraulically driven generator

ABSTRACT

Hydraulic system for driving an auxiliary power source is provided, which is specifically adapted for use with a system for controlling hydraulically driven AC generator. The system includes a hydraulic pump and hydraulic motor that are connected by a fluid circuit. The hydraulic motor drivably connected to an AC generator and is operated in a manner to generate a stable AC power output. The system may include a valve which bypasses fluid around the motor or a variable displacement pump so that the fluid flow rate through the hydraulic motor is controlled in a manner to maintain the desired AC generator output level. Sensors are further provided measuring operating parameters of the system so that the controller can maintain desired operating condition limits

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation in part of U.S. application Ser. No.11/275,574 filed Jan. 17, 2006.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to an electronic control for hydraulicsystem, and more particularly to precision control of hydraulicallydriven generators for stabilizing frequency and voltage outputcharacteristics.

2. Background Art

Most engine driven vehicles utilize an internal combustion engine as theprimary power source for propelling a vehicle. However, numerous modulesand devices for the vehicle as well as the engine require electricalpower. Typically, a rechargeable battery is provided with the vehicle asa basic power supply. The battery power supply system provides directcurrent (DC) electrical power for starting the vehicle engine and foroperating certain DC compatible electrical loads when the vehicle is notrunning. The battery is recharged to maintain power by an alternatorcoupled to and driven by the engine when the vehicle is running.Concurrently, the alternator also provides DC electrical power to thevehicle electrical loads.

With the advent of electronics in today's modern vehicle, groundvehicles, boats and aircraft alike, the amount of electrical loads whichrequire power has significantly increased. Moreover, many variousauxiliary electrical loads are dependent upon stable alternating current(AC), for example, rescue and military vehicles having AC poweredcommunications equipment. Additionally, many other vehicles, such asutility and telephone company repair and maintenance vehicles andvehicles providing electrical welding equipment, are increasinglyutilizing AC equipment dependent upon clean AC power.

Various systems have been proposed for alleviating the complication ofoperating both AC and DC powered electrical equipment. One such systeminvolves driving an auxiliary AC generator from the vehicle's engine orprincipal power plant. This can be accomplished by connecting thegenerator to a power take off or to any other suitable connection toengine output. While this will indeed operate a generator, variations inengine speed will wreak havoc with characteristics of power output andtherefore with equipment which is dependent upon stable voltage andfrequency characteristics of electrical power.

Accordingly, various systems have been proposed to control speed of anAC generator. One such system utilizes a hydraulic circuit having avalve for supplying a constant rate of fluid flow to a hydraulic motor.The hydraulic motor in turn drives a generator for supplying AC power tocertain AC compatible electrical loads. However, such systems can havedifficulty maintaining precise frequency output for controlling the mostsensitive AC equipment and are often susceptible to premature mechanicalfailure.

SUMMARY OF THE INVENTION

Accordingly, it is an aspect of the present invention to provide ahydraulic control system for generating precise electrical outputcharacteristics, particularly frequency and voltage output, along withprolonging the life of the system, thus reducing warranty returns andcosts associated therewith.

A hydraulic control system for driving an auxiliary power source,located aboard a motor vehicle having a primary power source, atconstant speed despite fluctuations in rotational speed of the primarypower source is provided. The system may include a hydraulic pump, ahydraulic motor, a fluid circuit, a control valve assembly, and acontrol circuit. Control valve may be proportional, and/or compensationor a combination of both. The hydraulic pump may be drivably connectableto the primary power source and can have an inlet for receiving fluidfor pumping and an outlet for discharging pumped fluid under pressure.The hydraulic motor may be drivably connectable to the auxiliary powersource and can have an inlet for receiving fluid under pressure and anoutlet for discharging spent fluid. The fluid circuit may include asupply conduit for conducting fluid discharged by the pump to the motor,a return conduit for returning fluid discharged by the motor to thepump, and a bypass conduit for conducting fluid discharged by the pumpdirectly to the return conduit, bypassing the motor, and returning fluidto the pump.

The control valve assembly can be disposed serially and/or parallel withrespect to the supply conduit and interposed between the outlet of thepump and the inlet of the motor. The control valve assembly may have ahousing including a valve chamber, a valve disposed within the valvechamber for apportioning the flow of fluid between the supply conduitand the bypass conduit, a solenoid drivably connectable to the valve forselectively moving the valve incrementally within the valve chamber froman open position to a closed position. Moreover, a first fluid passagemay be provided in fluid communication with the valve chamber and thesupply conduit going to the motor, while a second fluid passage may beprovided in fluid communication with the valve chamber and the bypassconduit. The valve can selectively close and open the first fluidpassage and the second fluid passage proportionally dividing the flow offluid there between.

The control circuit may be in electrical communication with the valveassembly for controlling the valve assembly and hence the fluid flowwithin the first fluid passage to the motor supply conduit and thesecond fluid passage to the bypass conduit. Further, the control circuitmay include a sensor electrically coupled to the auxiliary power sourcefor determining output frequency and/or voltage of the auxiliary powersource. A reference signal generator for generating a reference signalindicative of a predetermined output frequency may also be provided.Additionally, the control circuit can include a comparing subcircuit forcomparing sensed output frequency and/or voltage with the referencesignal, and for generating a control signal controlling the valveassembly such that the supply of fluid conducted to the supply conduitis sufficient to maintain desired output frequency and/or voltage.

Moreover, the control circuit of the hydraulic control system mayfurther include a temperature sensor disposed in the fluid circuit forsensing hydraulic fluid temperature. A system controller having a fluidpre-heating subcircuit may be provided for generating a control signalcontrolling the valve assembly such that fluid bypasses the hydraulicmotor entirely until safe fluid temperature is obtained. Further, thesystem controller may further include a power ramping subcircuit forgenerating a control signal controlling the valve assembly whensufficient fluid temperature is obtained such that power is suppliedgradually to the hydraulic motor.

Furthermore, the system controller may include an overtemperatureshutdown subcircuit for generating a control signal controlling thevalve assembly when fluid temperature becomes too hot for safe operationsuch that fluid bypasses the hydraulic motor, shutting down theauxiliary power source. Additionally, the control circuit can beequipped with an emergency override accessible by an operator forinstructing the system controller to continue system operation althoughunsafe operating conditions exist that may damage the unit.

It is another aspect of the present invention to provide a hydrauliccontrol system that senses fluid pressure in the fluid circuit andautomatically engages the auxiliary electrical system to power certainelectrical loads, provided safe operating temperatures are obtained.

Accordingly, the control circuit of the hydraulic control system mayfurther include a pressure sensor for determining sufficient hydraulicpressure for commencing system operation. The pressure sensor can causesystem operation to begin when hydraulic pressure is sufficient, andcan, correspondingly, cause system operation to shut down when hydraulicpressure is deficient.

In an alternative embodiment of the invention, the then control valveassembly can be eliminated. Rather than bypassing the pump output aboutthe hydraulic motor, a variable displacement of the pump is utilizedhaving a pump displacement input. The effect of displacement of the pumpcan be varied in order to achieve a desired hydraulic motor inputpressure automatically increasing pump displacement when the pressuredrops and then decreasing pump displacement when the hydraulic motorinput pressure exceeds a specified level.

In a particular construction of the present invention, the hydraulicmotor, the associated auxiliary power source and much of the controlcircuit is located in a module suitable for being located on theexterior of a vehicle.

Yet another aspect of the present invention is to control operation ofthe hydraulic circuit to perform under safe operating conditions.

Therefore, a method, according to the invention, for operating ahydraulic control system may include sensing hydraulic fluid temperaturein a fluid circuit, warming hydraulic fluid by circulating the fluidthrough portions of the fluid circuit bypassing a hydraulic motor, ifsensed fluid temperature is below safe operating temperature, andsupplying hydraulic fluid slowly through to the hydraulic motor oncehydraulic fluid reaches safe operating temperature to gradually bringthe motor up to desired speed so that full power operation can commence.

Warming the hydraulic fluid may involve maintaining open anelectronically controlled hydraulic valve disposed within the fluidcircuit such that fluid is directed entirely to a bypass conduit.Supplying hydraulic fluid slowly to the hydraulic motor may involvegradually closing an electronically controlled hydraulic valve disposedwithin the fluid circuit such that fluid is gradually conducted througha motor supply conduit in fluid communication with the hydraulic motorin order to gradually apply power to the motor.

Moreover, the method for operating the hydraulic control system mayfurther include sensing hydraulic motor output characteristics andapportioning fluid flow to the hydraulic motor in order to maintainconstant motor output characteristics. Sensing hydraulic motor outputcharacteristics may involve sensing electrical output characteristics ofa generator driven by the hydraulic motor. Apportioning may involvecomparing sensed output characteristics with predetermined outputcharacteristics, generating a control signal based on the comparison,and selectively controlling an electronically controlled hydraulic valveto move incrementally within a valve chamber such that fluid isproportionally divided between a motor supply conduit in fluidcommunication with the hydraulic motor and a bypass conduit, whichbypasses the hydraulic motor.

Further, the method of operating the hydraulic control system mayinclude preventing over-temperature damage to the hydraulic system whenthe sensed fluid temperature exceeds safe operating temperature.Preventing over-temperature damage may involve annunciating theexistence of over-temperature conditions to an operator when a firsthigh temperature is obtained, triggering a timer to begin counting downa specified time when a second high temperature is obtained, andbypassing all fluid flow to the motor when the timer has expired.Bypassing all fluid flow to the motor can involve opening anelectronically controlled hydraulic valve disposed within the fluidcircuit such that fluid is directed entirely to a bypass conduit.Additionally, the method may include overriding the bypassing step uponreceipt of an emergency override instruction from an operator to preventshutdown and keep the system operating.

Furthermore, the method of operating the hydraulic control system mayalso include sensing fluid pressure in the fluid circuit, commencingoperation of an auxiliary power source if sensed fluid pressure issufficient by controlling a hydraulic valve to meter fluid to thehydraulic motor, which drives the auxiliary power source, and ceasingoperation of an auxiliary power source if sensed fluid pressure isdeficient by fully opening the valve to bypass all fluid flow to themotor.

Still another aspect of the invention is to provide annunciation ofauxiliary power source output characteristics.

Still yet a further aspect of the invention is that acceleration of theauxiliary power source from the stopped condition, as well as coldtemperature condition, be gradual.

These and other aspects, objects, features and advantages of the presentinvention will become more clearly understood and appreciated from areview of the following detailed description of the preferredembodiments and appended claims, and by reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention which are believed to be novel areset forth with particularity in the appended claims. The presentinvention, both as to its organization and manner of operation, togetherwith further object and advantages thereof, may best be understood withreference to the following description, taken in connection with theaccompanying drawings in which:

FIG. 1 is a schematic diagram of a hydraulic circuit exhibited in anexemplary control system according to an aspect of the presentinvention;

FIG. 2 is a schematic diagram of an alternate hydraulic circuitexhibited in an exemplary control system according to an aspect of thepresent invention;

FIG. 3 is a schematic diagram of a second alternative embodiment of ahydraulically driven generator and the associated control circuit inaccordance with another aspect of the present invention;

FIG. 4 is a graph generally displaying system characteristics duringcold start operation according to an aspect of the present invention;

FIG. 5 is a schematic diagram of a third alternative embodiment of ahydraulically driven generator and the associated control circuit inaccordance with another aspect of the present invention; and

FIG. 6 is an illustration of auxiliary module unit suitable for mountinga hydraulic driven generator of the present invention to the exterior ofa motor vehicle.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

As required, detailed embodiments of the present invention are disclosedherein. However, it is to be understood that the disclosed embodimentsare merely exemplary of an invention that may be embodied in various andalternative forms. Therefore, specific functional details disclosedherein are not to be interpreted as limiting, but merely as arepresentative basis for the claims and/or as a representative basis forteaching one skilled in the art to variously employ the presentinvention.

A hydraulic control system 10, according to an aspect of the presentinvention, is illustrated in FIGS. 1 and 2. FIG. 1 generally depicts ahydraulic circuit 12 for the hydraulic control system 10, while FIG. 2generally depicts a control circuit 14 for the hydraulic control system10.

Referring first to FIG. 1, the hydraulic circuit 12 of the system 10 ispowered by a hydraulic pump 16, having an inlet 18 for receiving fluidfor pumping and an outlet 20 for discharging pumped fluid underpressure. The hydraulic pump 16 can be a variable displacement typepump, a fixed displacement type pump, or the like, for pumpingpressurized fluid throughout a fluid circuit 22. The hydraulic pump 16can be driven by a primary power source 24, such as a vehicle powertake-off (PTO), belt drive, gasoline engine, diesel engine, or anysimilar input. A hydraulic motor 26, having an inlet 28 for receivingfluid under pressure and an outlet 30 for discharging spent fluid, canbe disposed within the hydraulic circuit 12, as shown. The hydraulicmotor 26 drives an auxiliary power source 32, which provides electricalor mechanical power to vehicle loads or devices (not shown). Forexample, the auxiliary power source 32 can be an AC generator, amechanical drive system, or other source requiring constant rotationalspeed. The hydraulic motor 26 can be drivably connected to the auxiliarypower source 32 through a shaft 34 (as shown in FIGS. 1 and 2), or abelt or other means of power transmission (not illustrated). Moreover,the hydraulic motor 26 can be a fixed displacement gear type motor, vanetype motor, piston type motor, or the like.

The fluid circuit 22 can include a supply conduit 36, a return conduit38, and a bypass conduit 40. The supply conduit 36 can be divided intoat least two sections—a valve supply conduit 36 a and a motor supplyconduit 36 b. The supply conduit 36 conducts fluid discharged by thepump 16 to the motor 26, while the return conduit 38 returns fluiddischarged by the motor 26 to the pump 16. The bypass conduit 40,meanwhile, can be disposed in the fluid circuit 22 to conduct fluiddischarged by the pump 16 directly to the return conduit 38, bypassingthe motor 26, where the fluid is subsequently returned to the pump 16.

The system 10 preferably includes a control valve assembly 42, such asan electro-hydraulic control valve assembly, controlled by a systemcontroller 44 (shown in FIG. 2). The control valve assembly 42 can bedisposed serially and/or parallel with respect to the supply conduit 36such that it is interposed between the outlet 20 of the pump and theinlet 28 of the motor. The control valve assembly 42 may include ahousing 46 generally enclosing a valve chamber 48. A valve 50, whichshuttles back and forth between an open position and a closed position,may be disposed within the valve chamber 48. The control valve assembly42 may further include a first fluid passage 52 and a second fluidpassage 54. Further, the control valve assembly 42 can be disposedwithin the hydraulic circuit 12 such that the first fluid passage 52 isin fluid communication with the valve chamber 48 and the motor supplyconduit 36 b, while the second fluid passage 54 is in fluidcommunication with the valve chamber 48 and the bypass conduit 40. Asolenoid 56 or other electronic or electromechanical device can bedrivably connected to the valve 50 for selectively moving the valve 50incrementally within the valve chamber 48 from the open position to theclosed position. The solenoid 56 can be in electrical communication withthe system controller 44, which drives the solenoid 56. Accordingly, thesystem controller 44 can communicate with the control valve assembly 42such that the valve 50 selectively closes and opens the first fluidpassage 52 and the second fluid passage 54, thereby dividing fluid flowproportionally therebetween.

As the valve 50 divides the flow of hydraulic fluid between the firstfluid passage 52 and the second fluid passage 54, the fluid can becorrespondingly directed to the motor supply conduit 36 b and the bypassconduit 40, respectively. Fluid directed to the motor supply conduit 36b may be supplied to, and discharged by, the motor 26 for powering theauxiliary power source 32 before returning to the pump 16 via the returnconduit 38. Fluid directed to the bypass conduit 40 can bypass the motor26 completely as it is steered immediately to the return conduit 38,without being supplied to the motor 26, for restoring to the pump 16.

Optionally, the hydraulic circuit 12 may include a fluid reservoir 58and a pump case drain 60 disposed at the pump 16, a motor case drain 62disposed at the motor 26, or both. The fluid reservoir 58 can be influid communication with the fluid circuit 22 and maintains hydraulicfluid on reserve that can be introduced to the pump 16 via the returnconduit 38. In an embodiment of the present invention, possible casedrain flow from the pump 16 and the motor 26 can be directed back to thefluid reservoir 58 through drain conduits 64 a-b (as illustrated inFIGS. 1 and 3). Fluid flow in the return conduit 38 can be directedthrough a venturi boost 66, where fluid from the fluid reservoir 58 maybe drawn into the return conduit 38 to replace that lost from the casedrain flow, and supplied back to the pump 16. Alternatively, the drainconduits 64 a-b can be disposed in the fluid circuit 22 such that casedrain flow can be pulled directly to the return conduit 38 by theventuri boost 66, without first being directed to the fluid reservoir 58(as shown in FIG. 1).

Additionally, the hydraulic circuit 12 may also include a fluid filter68 and a fluid cooler 70. The fluid filter 68 and the fluid cooler 70are preferably disposed serially and/or parallel with respect to thereturn conduit 38. However, it is to be understood that the fluid filter68 and fluid cooler 70 can be disposed anywhere within the fluid circuit22 without departing from the scope of the present invention. Impuritiesintroduced into the hydraulic fluid as it gets cycled through the fluidcircuit 22 can be filtered by the fluid filter 68. The fluid cooler 70,on the other hand, can cool fluid that passes there through.Accordingly, the fluid cooler 70 may include a heat exchanger (notseparately shown) for dissipating heat to ambient air, an electricallyoperated fan 72 disposed adjacent the heat exchanger for forcing ambientair through the heat exchanger, and a thermostat 74 (not separatelyshown in FIG. 1) which controls fan operation when fluid containedwithin the fluid cooler 70 exceeds a predetermined temperature. Thethermostat 74 can directly control the fan 72, or, alternatively, thethermostat 74 can control fan operation through the system controller44. For example, the thermostat 74 and the fan 72 may be in electricalcommunication with the system controller 44. The system controller 44may receive temperature readings of the fluid in the fluid cooler 70from the thermostat 74. Correspondingly, the system controller 44 canoperate the fan 72 by transmitting a fan control signal 76 to the fan 72when fluid contained within the fluid cooler 70 exceeds thepredetermined temperature.

The system 10, according to an aspect of the present invention, may alsoinclude a pressure sensor 78 a, a temperature sensor 78 b, a fluid levelsensor 78 c, an electrical output 78 d (FIG. 2 only), and a speed sensor78 e, collectively referred to as system control sensors 78. Each of thecontrol sensors 78 can be provided as part of the control circuit 14,shown in FIG. 2, and are configured to provide control inputs to thesystem controller 44. The control sensors 78 can be deployed throughoutthe system 10 to measure system vitals and assure the auxiliary powersource 32 is driven at constant speeds.

Referring back to FIG. 1, the pressure sensor 78 a can be disposed alongthe valve supply conduit 36 a proximate the pump 16 to sense hydraulicpressure. However, it is to be understood that there are many otherlocations in the fluid circuit 22 for positioning the pressure sensor 78a so long as it can accurately sense that the pump 16 is operating.Similarly, the temperature sensor 78 b can be disposed along the fluidcircuit 22 to monitor hydraulic fluid temperature. The temperaturesensor 78 b can be separate from the thermostat 74 and thus provideseparate input to the system controller 44, or, alternatively, thetemperature sensor can be the same as the thermostat. The fluid levelsensor 78 c can be disposed within the fluid reservoir 58 to monitor thelevel of hydraulic fluid within the reservoir 58. If the fluid levelbecomes low, the system controller 44 may announce a tell-tale alarm,light or other warning, to the operator. If the fluid level becomesextremely low, the system controller 44 may cause the system 10 to shutdown entirely to prevent damage to the pump 16.

In an embodiment of the present invention, the auxiliary power source 32can be an AC generator. Accordingly, the electrical output 78 d can be acurrent sensor, voltage sensor, or both for monitoring the generator'soperating characteristics, including current, voltage and frequency. Theelectrical output 78 e can be connected to output conductors 80 of thegenerator to sense the generator operating parameters. Alternatively,the speed sensor 78 d may be provided to monitor rotational speed of themotor 26 and the shaft 34, by sensing each revolution of the shaft 34,in order to provide controlled input to the system controller 44relating to operation of the hydraulic motor 26.

Referring now to FIG. 2, the control circuit 14 will be described infurther detail with reference to an AC generator as the driven auxiliarypower source 32, although other applications referred to in the detaileddescription are also possible. As previously described, the controlcircuit 14 may include the system controller 44 and one or more of thecontrol sensors 78, as well as a reference signal generator 82. Thesystem controller 44 can be a programmable controller having amicroprocessor (not separately shown) that implements control algorithmsfor the control of the generator output, namely voltage and frequency.The system controller 44 controls the generator output by applying acontrol output signal 84 to the control valve assembly 42, directing thevalve assembly 42 to meter fluid, and hence power, to the motor 26 fordriving the generator. The system controller 44 varies the powersupplied to the hydraulic motor 26 through the use of the control outputsignal 84. Accordingly, the control output signal 84 can be apulse-width modulated voltage waveform or a variable DC output voltageapplied to the solenoid 56 of the valve assembly 42.

Vehicles today often rely on sensitive and delicate electronicsequipment, wherein only the cleanest of power is acceptable foroperation. Very little variance in the output frequency of an ACgenerator is tolerable in order to operate various devices such ascomputers and communications equipment. Merely close frequency output inrelation to desired frequency output is not good enough. Accordingly, itmay be desirable to compare actually frequency with a predeterminedfrequency, rather than merely relying on sensed motor speed as anindirect method of determining the generator's output characteristics.Of course, it is to be understood that sensing rotational speed of themotor 26 may be adequate in certain applications. Nonetheless, in anembodiment of the present invention, the electrical output 78 d can beelectrically coupled to the generator. The reference signal generator 82can be in electrical communication with the system controller 44 andgenerates a reference signal 86 indicative of the predetermined outputfrequency. The system controller 44 may include a comparing subcircuit88 that implements control algorithms for comparing sensed outputfrequency with the reference signal 86. The comparing subcircuit 88 canthen generate and transmit control output signals for controlling thevalve assembly 42 such that the supply of fluid conducted to the motor26 be sufficient to maintain desired generator output frequency.

The system controller 44, constructed in accordance with an exemplaryembodiment of the present invention, may also implement additionalcontrol algorithms for the electrical or mechanical system's outputfunctions in response to load variations, physical changes in theelectrical or mechanical system's operating environment or equipment,and communications from the user or other electronic modules. As theload on the electrical or mechanical system is increased or decreased,or the hydraulic fluid viscosity changes due to temperature fluctuationsand such, or the operating characteristics of the pump 16, motor 26, orthe valve assembly 42 change due to ambient conditions or wear, thesystem controller 44 can further adjust outputs to maintain consistentoperation of the electrical or mechanical system.

The control circuit 14 may further include an operator interface module90 enabling an operator of the system 10 to communicate with the systemcontroller 44 through a bi-directional asynchronous serialcommunications interface. The interface module 90 can display systemoperating parameters through an information display 92. As non-limitingexamples, the operating parameters displayed may include output voltage,frequency, current, hydraulic fluid temperature, total operating hours,and the like. The interface module 90 can also display or announce alarmconditions or faults detected by the system controller 44 and permit theoperator to interact with the system controller 44 and influence theoperation of the auxiliary power source 32. The alarm conditions can beannounced by an audible alert 94 included in the interface module 90.The operator may also influence the configuration of the systemcontroller 44. For example, the operator may turn the hydraulicallypowered system 10 on or off through an ON/OFF switch 96. Moreover, theoperator may configure the system controller 44 to automatically turnthe auxiliary power source 32 on when sufficient hydraulic pressure isdetected. Further, the operator can instruct the system controller 44 topurge air from the hydraulic lines, and configure the maximum expectedoutput values to be controlled by the system. The operator communicateswith the system controller 44 through a keypad 98 disposed in theinterface module 90. Furthermore, multiple interface modules may belinked together to add multiple operator interfaces if desired.

When the electrical or mechanical system to be driven is idle or shutdown, the valve 50 can be normally fully open, directing all fluid flowinto the bypass conduit 40, and depriving the motor 26 of power. At theoperator's request through the interface module 90, power can be meteredto the motor 26 by incrementally closing the valve 50, which beginsdiverting some amount of fluid flow to the motor 26. The more the valve50 is closed, the more power can be provided to the motor 26, therebyactivating the electrical or mechanical system.

Alternatively, the application of hydraulic pressure to the fluidcircuit 22 may be interpreted by the system controller 44 as a commandto commence electrical or mechanical system operation. The operator maywish to configure the system controller 44 to automatically power theauxiliary power source 32 when the pump 16 is operating. If pressuresufficient for system operation is detected by the pressure sensor 78 a,system operation can automatically commence without further instructionfrom the operator. On the other hand, if the hydraulic pressure fallsbelow that required for system operation, the system controller 44 candirect the valve 50 to open fully, diverting all fluid flow into thebypass conduit 40, thereby shutting down motor operation.

The system controller 44 may further include a fluid pre-heatingsubcircuit 100. If the temperature sensor 78 b detects that hydraulicfluid in the system 10 is too cold for normal operation, the systemcontroller 44 can implement the fluid pre-heating subcircuit 100 to warmthe fluid to a safe operating temperature. The fluid pre-heatingsubcircuit 100 can generate control output signals for controlling thevalve assembly 42 such that fluid bypasses the hydraulic motor 26entirely until safe fluid operating temperature is obtained, avoidingdamage to the mechanical components. The system controller 44 can holdthe valve 50 fully open to circulate the hydraulic fluid through thebypass conduit 40. Normal mechanical friction will warm the fluid untilit reaches a first predetermined temperature, at which point the valve50 can be opened only enough to pass the warming fluid slowly throughthe motor 26. Normal mechanical friction will warm the fluid furtheruntil it reaches a second predetermined temperature, at which point fullpower operation can commence.

The application of the fluid pre-heating subcircuit 100 can beincredibly advantageous in extremely low temperatures where thehydraulic fluid can partially congeal. If fluid were permitted to passthrough the motor 26 immediately, prior to frictional warming throughthe bypass conduit 40, lumps of congealed fluid can momentarily obstructthe motor gears causing the motor 26 to briefly decelerate and thenaccelerate. The deceleration and acceleration caused by lumps in thefluid passing through the motor gears occurs almost instantaneously,resulting in large voltage spikes at the output of the auxiliary powersource 32 (in the case of a generator). The duration of the voltagespike is very abrupt and the magnitude of the voltage spike can besufficient to damage various electrical loads. The fluid pre-heatsubcircuit 100 substantially minimizes this occurrence reducing warrantyclaims and the costs associated with, while greatly increasing customersatisfaction and good will.

Once pressure and temperature are sufficient, full system operation canbegin. In order to bring the system 10 up to power, the systemcontroller 44 may utilize a power ramping subcircuit 102. The powerramping subcircuit 102 can enable the system controller 44 to slowlyclose the valve 50 so as to gradually apply power to the hydraulic motor26. This gradual application of power allows the system 10 to gentlyovercome inertial effects, greatly reducing wear and increasing systemcomponent lifetimes.

With reference now to FIG. 4, a graphical representation of cold startoperation parameters of the system, utilizing the fluid pre-heatingsubcircuit 100 and the power ramping subcircuit 102, is illustrated.Pump speed 101 generally depicts revolutions per minute (RPMs) of thehydraulic pump 16 over time at initial system cold temperature start-up.Pump speed 101 can fluctuate over time as the vehicle engine speedfluctuates. Fluid temperature 103 generally depicts temperature of thefluid in the fluid circuit 22 during cold start operation. At coldstart, hydraulic fluid can bypass the motor 26 until it warms to asufficient temperature, at which point fluid is slowly diverted to themotor 26 to gradually supply power to the system. During this ramp-up,fluid temperature 103 can increase further permitting full systemoperation to begin. Motor speed 105 generally depicts operation of themotor (in RPMs) during cold start. The motor 26 can get little or nopower, while the fluid warms as it circulates through the bypass conduit40. Once a desired temperature is obtained, motor speed 105 slowly rampsup as fluid is gradually supplied to the motor 26. Once full systemoperation commences, motor speed 105 remains substantially constant,despite fluctuations in engine speed and hence pump speed 101.

Further, the system controller 44 may include an overtemperatureshut-down subcircuit. When the temperature of the hydraulic fluidexceeds safe operating conditions, the overtemperature shut-downsubcircuit 104 can notify the operator of the electrical or mechanicalsystem that excessive temperatures are being detected, and action may berequired to prevent damage to the system 10. When the temperatureexceeds yet another temperature threshold, the overtemperature shut-downsubcircuit 104 can start an internal timer. If the timer expires, thevalve 50 may be fully opened by the overtemperature shut-down subcircuit104, bypassing all fluid flow and shutting down the hydraulic system 10unless the operator issues an emergency override instruction through thekeypad 98 to prevent the shutdown and keep the electrical or mechanicalsystem operating.

The system controller 44 may also have the ability to record allabnormal conditions and faults to a diagnostic memory 106. The faultscan be retrieved from the diagnostic memory 106 by the operator anddisplayed by the interface module 90 to evaluate the conditions seen bythe system 10 and assist in any necessary troubleshooting. Recordedconditions may include, but are not limited to, valve voltage faults,valve current faults, over current faults, current sensing faults,temperature sensing faults, ground faults, number of over temperatureoverrides, fan faults, voltage sensing faults, hours run with overtemperature, highest recorded frequency, highest recorded voltage,highest measured current, highest measured temperature, hours run withovercurrent, hours on oil filter, calibration values, maximum currentvalues, and total hours.

Yet another advantage of the hydraulic control system 10, according tothe present invention is that it can be a self-contained system that canalso be readily retrofit to a vehicle having a power take of, enginedriven belt drive, or any other power supply source. Moreover, thesystem 10 may include a circuit breaker 108 as yet another protectivefeature. The circuit breaker 108 may be located in series with outputconductors 80 connected to output terminals of the generator. Thecircuit breaker 108 can operate conventionally by opening an externalcircuit (not shown), which is connected to the conductors to conductelectrical power to powered equipment.

A general overview of the operation of the hydraulic system electroniccontrol, according to a certain embodiment of the present invention, isprovided below. The system controller 44 can sense adequate operatingpressure in the fluid circuit 22. If the system controller 44 does notautomatically interpret sufficient pressure as a command to commenceoperation, it can wait to receive a command signal from an input,operator, or other electronic module to activate the hydraulicallypowered mechanical or electrical system. The system controller 44 canthen check the status and values of the control inputs to ensureoperation will be safe and effective. If the hydraulic fluid temperatureis too low, the fluid pre-heat subcircuit 100 can cause the fluid towarm to safe operating temperatures. The system controller 44 can thengradually apply power to the hydraulic motor 26 by slowly closing thevalve 50, according to the power ramping subcircuit 102. Appropriatecontrol signals can be applied by the system controller 44 to outputs inresponse to the control inputs to achieve the desired control andfunction of the system 10. If the hydraulic fluid temperature becomestoo high for safe operation, the overtemperature shut-down subcircuit104 can be implemented to shut down the operation of the electrical ormechanical system. The system's operating parameters may be sent viaserial communications using a proprietary protocol to the operatorinterface module 90 or other electronic module. If a command is receivedfrom the operator or other electronic module to cease operation, or thehydraulic pressure falls below that required for operation, the systemcontroller 44 can shut down the electrical or mechanical system by fullyopening the valve 50, bypassing all hydraulic fluid flow to the motor26.

A third embodiment of the invention is illustrated in FIG. 5. Ahydraulically driven generator system 110 is similar to system 10described with reference to FIG. 1, however rather than using a controlvalve assembly 42 to regulate the amount of the output of pump 16 thatpasses through hydraulic motor 26, a variable displacement pump 112 isutilized which has an external input which enables the control system tovary the pump displacement to achieve the desired flow rate needed forhydraulic motor 36. The hydraulic control circuit 114 of the FIG. 5embodiment is otherwise generally similar to the control system 12utilized in the FIG. 1 embodiment and like components function in asimilar manner as described previously.

In operation the output from pump 112 provides hydraulic fluid tohydraulic motor 26. As previously described, the control valve 42 isutilized in the FIG. 1 embodiment is not longer required provided thepump minimum displacement is sufficiently low. If the minimum pumpdisplacement is substantial, i.e., over 20% of maximum pumpdisplacement, a control valve 42 as previously described can be add inorder to deactivate the motor 26 at desired times. When control valve 42is not used an optional pressure regulator 116 can be provided tomaintain desired minimum back pressure on the outlet of pump 112 whichis sufficient to operate pump displacement control 120 which is suppliedwith hydraulic fluid via line 118.

A pump displacement control 120 cooperates with pump 112 to vary thedisplacement of the pump as needed. The pump displacement control 120can have a hydraulic output or alternatively a mechanical output asdictated by the pump design. The pump displacement control 120 variesthe pump displacement as a function of a control signal 84 received fromsystem controller 44 illustrated in FIG. 2. The pump displacementcontrol 120 is hydraulically powered, alternatively an electricallyoperated actuator such as a stepper motor could be used to vary pumpdisplacement. The hydraulically driven generator system 110 of the FIG.5 embodiment is designed to have reduced pumping losses and associatedenergy consumption when compared to the system 10 of FIG. 1 in whichhigh pressure fluid is routinely bypassed about the hydraulic motor athigh pump speed conditions.

FIG. 6 illustrates a preferred packaging module 122 for mounting thehydraulically driven generator of the present invention to a motorvehicle. Typically, there is insufficient space in the vehicle enginecompartment or adjacent the vehicle drive train to mount a hydraulicmotor and associated generator of the present invention inside the bodyof a vehicle. Module assembly 122 is suitable for attachment to theexterior or a motor vehicle. A large portion of the hydraulically drivengenerator system can be mounted within module assembly 122. The portionof the system suitable for mounting outside module 122 is illustrated inphantom outline in FIG. 5 by reference number 124. Preferably thevariable displacement pump 112 and the associated pump displacementcontrol 120 will be mounted directly to the power source such asinternal combustion engine or a power takeoff associated with aninternal combustion engine of the vehicle. Motor 26 and generator 32 aremounted internally in module 122 as are the other components identifiedin region 124 of the FIG. 5.

Module 122 when mounted external to the vehicle not only eliminatesspace problems but further facilitates dissipating any excess heatgenerated by the hydraulic pump 112, motor 26 and generator 32 via afluid cooler 70. The module 122 can be provided with an open grate top126 as illustrated which allows air to freely circulate through themodule and provide a non-slip working surface for the system user.Preferably, the module 122 will be provided with a cooling fan 72forcing cooling air about the system components.

While embodiments of the invention have been illustrated and described,it is not intended that these embodiments illustrate and describe allpossible forms of the invention. Rather, the words used in thespecification are words of description rather than limitation, and it isunderstood that various changes may be made without departing from thespirit and scope of the invention.

1. A hydraulic system for driving an auxiliary power source, locatedaboard a motor vehicle having a primary power source, at a substantiallyconstant speed despite fluctuations in rotational speed of the primarypower source, the system comprising: a variable displacement hydraulicpump drivably connectable to the primary power source, the hydraulicpump having an inlet for receiving fluid, an outlet for dischargingfluid under pressure and a pump displacement input; a hydraulic motordrivably connectable to an auxiliary power source, the hydraulic motorhaving an inlet for receiving fluid under pressure and an outlet fordischarging fluid; a fluid circuit including a supply conduit forconducting fluid discharged by the pump to the motor, a return conduitfor returning fluid discharged by the motor to the pump; a pumpdisplacement control cooperating with the pump displacement input inorder to vary the displacement of the pump; and a control circuit incommunication with the pump displacement control for controlling thepump output so that a desired hydraulic motor and associated auxiliarypower source speed can be maintained.
 2. The system of claim 1, whereinthe control circuit further comprises: an electrical output sensorelectrically coupled to the auxiliary power source for determiningoutput frequency of the auxiliary power source; and a reference signalgenerator for generating a reference signal indicative of a desiredoutput frequency wherein the control circuit compares the sensed outputfrequency and/or voltage with the referenced signal to vary the pumpdisplacement so that the supply of fluid to the motor is sufficient tomaintain the desired output frequency and/or voltage.
 3. The system ofclaim 1 wherein the control circuit further comprises: a speed sensorfor determining rotational speed of the hydraulic motor; and a referencesignal generator for generating a reference signal indicative of adesired hydraulic motor speed, wherein the control circuit comparessensed rotational speed of the motor with the reference signal togenerate an output signal to the pump displacement control so that thesupply of fluid to the motor is sufficient to maintain the desiredrotational speed of the motor and associated auxiliary power source. 4.The system according to claim 1, wherein the control circuit furthercomprises a temperature sensor disposed in the fluid circuit for sensinghydraulic fluid temperature wherein the control circuit limits the pumpdisplacement to limit pump output hydraulic motor until a desired safefluid temperature is obtained.
 5. The system according to claim 4,wherein the control circuit ramps up the speed of the motor as afunction of fluid temperature on system startup.
 6. The system of claim4, wherein the control circuit further provides an overtemperatureshutdown to restrict pump output in order to shut down the motor andassociated auxiliary power source when the fluid temperature becomes toohot for safe operation.
 7. The system of claim 6, wherein the controlcircuit further comprises: an emergency override accessible by theoperator to continue system operation in spite of an overtemperaturecondition.
 8. The system of claim 1 further comprising: a control valveinterposed in the fluid circuit between the variable displacement pumpand the hydraulic motor, the control valve having an outlet incommunication with the hydraulic motor and a bypass outlet incommunication with the fluid circuit downstream of the hydraulic motor;wherein the control circuit communications with the control valve tobypass fluid around the hydraulic motor in order to further limit therotation of the hydraulic motor.
 9. The system of claim 1 wherein thepump displacement control is hydraulically powered and has a mechanicaloutput cooperating with the variable displacement pump.
 10. The systemof claim 1 further comprising an AC generator providing an auxiliarypower source operatively driven by the hydraulic motor.
 11. The systemof claim 10 further comprising: a modular frame adapted to be affixed tothe exterior of a motor vehicle; wherein the hydraulic motor and the ACgenerator which is driven thereby is mounted to the modular frame. 12.The method for operating a hydraulic system for driving auxiliary powersource located aboard a motor vehicle having a primary power sourcedriving a pump which in turn drives a hydraulic motor coupled to theauxiliary power source and a control circuit for controlling the flow ofhydraulic fluid in a motor enabling the auxiliary power source to bemaintained at a desired rotational speed independent of primary powersource speed fluctuations, the method comprising: sensing the hydraulicfluid temperature in the fluid circuit; when the hydraulic fluid isbelow a desired operating temperature minimizing the pump displacementand in turn minimizing pump output to gradually warm the hydraulic fluidby circulating fluid internally within the hydraulic pump while limitingflow to the hydraulic motor; and gradually increasing the pumpdisplacement and the hydraulic pump fluid output which is supplied tothe hydraulic motor as a function of hydraulic fluid temperature inorder to gradually increase the speed and temperature of the hydraulicmotor.